Patients with pulmonary hypertension are a heterogenous group with respect to the etiology of the pulmonary vascular changes. The pulmonary vascular resistance is variable in its capacity to respond to stimuli. In general these patients have a difficult postoperative course from both a respiratory and cardiac viewpoint. Dobutamine and dopamine are the two main beta stimulators for low output postoperatively. Their effect on the pulmonary vascular system has not been well studied. We have studied a group of postoperative cardiac surgical patients with preoperative pulmonary hypertension. Dose-response curves for both dopamine and dobutamine were developed. Hemodynamic parameters were recorded and from these the systemic and pulmonary vascular resistances were calculated. While both drugs significantly lower systemic vascular resistance, only dopamine significantly reduces pulmonary resistance. We conclude that the use of dopamine in these patients can be advantageous in their postoperative management.